The present invention relates to an apparatus for detaching and attaching a counterweight provided in a construction machine such as a hydraulic excavator or a hydraulic crane, and, more specifically, to an apparatus for detaching and attaching a counterweight to and from a rear end portion of a frame.
Typically, a heavy-weighted work device such as a shovel or a crane is supported by a front portion of a frame of a construction machine such as a hydraulic excavator or a hydraulic crane. A counterweight is provided in a rear end portion of the frame in such a manner as to maintain equilibrium between the weight of the counterweight and the weight of the work device. For reducing the weight of the construction machine when transporting the machine to or out from a construction site, the counterweight is sometimes removed from the frame of the construction machine. To allow such removal, an apparatus that allows attachment and detachment of the counterweight is secured to a rear end portion of the frame. By means of the apparatus, the construction machine can be transported with the counterweight suspended from the frame. Also, the apparatus allows the counterweight to be attached to and detached from the construction machine in a state maintained on the ground surface.
Japanese Laid-Open Patent Publication No. 7-268908, for example, describes a configuration of this type of detaching/attaching apparatus. The apparatus includes a bracket secured to a rear end portion of a frame. A proximal portion of a pivotal arm is pivotally supported with respect to the bracket. A cylinder that causes pivoting of the pivotal arm is provided between the pivotal arm and the bracket. A counterweight is pivotally suspended from the pivotal arm through a connection tool at a position closer to the distal end of the pivotal arm than a connecting portion of the pivotal arm with respect to a piston rod of the cylinder. Through pivoting of the pivotal arm through the cylinder, the counterweight moves between a mounting position at the rear end portion of the frame and the ground surface.
In the apparatus, the counterweight is connected to the pivotal arm at the position closer to the distal end of the pivotal arm than the connecting portion of the pivotal arm with respect to the piston rod. Therefore, when the counterweight is raised or lowered, the torque generated by the cylinder acts on the pivotal arm at a position closer to the proximal end of the pivotal arm than the connecting portion of the pivotal arm with respect to the piston rod. This makes it necessary to employ a cylinder that generates great torque, which leads to enlargement of the apparatus. Also, the load of the counterweight acts on the pivotal arm at the position closer to the distal end of the pivotal arm than the connecting portion of the pivotal arm with respect to the piston rod. Since the pivotal arm functions as a cantilever in this case, bending load is concentrated on the distal end of the pivotal arm. Therefore, in order to enhance rigidity of a pivotal lever, the dimensions and the weight of the pivotal lever must be increased. This makes it necessary to employ a cylinder that outputs great torque.
Further, the counterweight of this apparatus is moved between the mounting position at the rear end portion of the frame and the ground surface through pivoting of the pivotal lever. Specifically, such movement of the counterweight between the rear end portion of the frame and the ground surface forms an arcuate path the radius of which corresponds to the entire length of the pivotal arm. However, the movement path of the counterweight makes it impossible to place the counterweight on the frame in a stable state or smoothly move the counterweight from the mounting surface of the frame to the ground surface. To solve the problems, it is necessary to ensure a clearance of a predetermined height between the counterweight and the frame by elevating the counterweight from the mounting surface of the frame. Nonetheless, the apparatus of this patent publication does not include a mechanism for selectively raising and lowering the counterweight with respect to the frame.
Thus, for satisfying the aforementioned necessity, the apparatus has a support pin that projects rearward from the rear end portion of the frame. An engagement hole engageable with the support pin is defined in the counterweight. Therefore, by placing the counterweight at the mounting position defined at the rear end portion of the frame and engaging the support pin of the frame with the engagement hole of the counterweight, the counterweight is suspended by the support pin. However, this structure cannot hold the counterweight stably at the rear end portion of the frame. Also, in order to bear the weight of the counterweight, the support pin and the peripheral structure around the support pin must be reinforced. This further complicates the configuration of the apparatus. Further, positioning between the engagement hole of the counterweight and the support pin is complicated.
Unlike the apparatus of Japanese Laid-Open Patent Publication No. 7-268908, an apparatus described in Japanese Laid-Open Patent Publication No. 8-333776 includes a mechanism that selectively raises and lowers a counterweight with respect to a frame. The apparatus has a bracket secured to a rear end portion of the frame. A central portion of a first arm member is pivotally supported with respect to the bracket. A first cylinder through which the first arm member is pivoted is arranged between a first end of the first arm member and the bracket. A central portion of a second arm member is pivotally supported with respect to a second end of the first arm member. A second cylinder through which the second arm member is pivoted is provided between a first end of the second arm member and the first arm member. A counterweight is pivotally suspended from a second end of the second arm member. The position of the counterweight when placed on a rear end portion of the frame is defined as a mounting position. The position of the counterweight when elevated from the mounting position through pivoting of the second arm member by the second cylinder is defined as a separating position. The counterweight is selectively raised and lowered between the mounting position at the rear end portion of the frame and the separating position above the mounting position. The counterweight moves also between the separating position and the ground surface through pivoting of the first arm member by the first cylinder.
In this apparatus, the first arm member and the second arm member are supported pivotally with respect to each other. Also, the drive cylinders are connected to the first ends of the first and second arm members and the opposing arm member or the counterweight is connected to the second ends of the arm members. Since, in this case, each of the arm members functions as a cantilever, bending load is concentrated on the distal ends of the arm members. This makes it necessary to employ cylinders that output great torque and enhance strength of each arm member. This complicates the configuration of the apparatus.